Copepod hatching success in marine ecosystems with high diatom concentrations

Production, Transport, Fate and Effects of Lipids in the Marine Environment

Lipids form energy storage depots, cellular barriers and signaling molecules. They are generated and metabolized by enzymes under the influence of biotic and abiotic factors, and some-the long-chain polyunsaturated ω3 and ω6 fatty acids and cholesterol-are essential for optimal health in marine organisms. In addition, lipids have direct and indirect roles in the control of buoyancy in marine fauna ranging from copepods to whales. Phytoplankton account for about half of the planet's carbon fixation, and about half of that carbon goes into lipids. Lipids are an important component of the ocean's ability to sequester carbon away from the atmosphere through sinking and especially after transfer to zooplankton. Phytoplankton are the main suppliers of ω3 polyunsaturated fatty acids (PUFAs) in the marine environment. They also supply cholesterol and many phytosterols to ocean ecosystems; however, genomics is indicating that members of the Cnidaria, Rotifera, Annelida, and Mollusca phyla also have the endogenous capacity for the de novo synthesis of ω3 PUFAs as well as phytosterols. It has been predicted that ω3 long-chain PUFAs will decrease in marine organisms with climate change, with implications for human consumption and for carbon sequestration; however, the responses of ω3 PUFA supply to future conditions are likely to be quite diverse.

Assessment of Hydrobiological and Soil Characteristics of Non-Fertilized, Earthen Fish Ponds in Sindh (Pakistan), Supplied with Seawater from Tidal Creeks

In this study, the suitability of four earthen, seawater ponds located in the Thatta district of Sindh province (Pakistan) was evaluated for the purpose of semi-intensive mariculture, which remains to be a severely underdeveloped branch of the agricultural industry of this populous Asian country. Initial pond soil probes were promising, as they showed a high clay and silt content. Monthly water samples were obtained in the year 2019 (from January to December), which allowed for the monitoring of water parameters, as well as the identification and relative quantification of planktic populations. As a result, the monthly variations of basic water parameters were found within optimal ranges for planktic growth (water temperature, salinity, pH, transparency, and dissolved oxygen). Bacillariophyta was the largest phytoplanktic group, with the most dominant species being Sundstroemia setigera, followed by the cyanobacteria Oscillatoria limosa. Copepoda was the most numerous group of identified zooplankton, followed by tintinnids and foraminiferans. Total suspended solids (TSS) calculations indicated up to nine-fold month-to-month reductions of planktic biomass, observed in the form of diminishing Bacillariophyta (December) and Copepoda (June and December). In conclusion, the studied ponds appear to be suitable for semi-intensive mariculture activity due to the abundance of diverse planktic forms (mainly Copepoda—preferable natural food for commercially important fish species), which was achieved even without the use of fertilizers. However, significant drops of planktic biomass may still occur, which implies the need for regular water monitoring procedures, which would in turn allow fish producers to implement periodical adjustments to the administered feeding rates with artificial diets.

Dietary bioaccumulation of UV-absorbing compounds, and post-ingestive fitness in larval planktotrophic crustaceans from coastal SW Atlantic

Increased ultraviolet radiation (UVR) is a major environmental stressor for marine organisms. The response of planktotrophic larvae of holo- and meroplanktonic crustaceans fed dietary algae grown under different light regimes and contents of UV-absorbing compounds (UACs), was experimentally evaluated. Paracalanus parvus copepodites and Cyrtograpsus angulatus zoeae were fed diatoms grown under two radiation treatments: PAR (400-700 nm, produced by 40 W cool-white fluorescent bulbs) and PAR + UVR (280-700 nm; adding Q-Pannel UV-A-340 lamps to PAR fluorescent bulbs). An absorption peak at 337 nm (UVR range) was observed only for larvae fed UVR-irradiated diatoms. After 144 h of ad libitum feeding, larvae were exposed to UVR for 24 h. Mortality rates were ~80% in individuals fed PAR-reared microalgae, and ~10% for those fed UV-irradiated microalgae. Results point to the importance of UACs conferring some tolerance to planktotrophic larvae under increased environmental UVR stress. Yet, acquired tolerance is differential among larvae, with implications for zooplankton ecology.

A New Type of Ecological Floating Bed Based on Ornamental Plants Experimented in an Artificially Made Eutrophic Water Body in the Laboratory for Nutrient Removal

In this study, a new type of ecological floating bed (NT-EFB) employing ornamental plants (either Spathiphyllum floribundum, Hydrocotyle sibthorpioids, Chlorophytum comosum or Peperomia obtusifolia) was designed to purify confected eutrophic water for 39 days. The growth characteristics of the plants and the effect of water treatment were analyzed and compared. The results showed that: (1) all the four ornamental plants examined survived well in the eutrophic water and an increase of plant biomass was observed; (2) the degradation efficiency of TOC by adding plants was about 85.0%; (3) the removal rate of NH₄⁺-N was about 97.0%; (4) all the four plants can be used as floating bed plants to treat eutrophic water and Hydrocotyle sibthorpioids had the best growth characteristics and treatment efficiency. The study provides an adequate reference for the treatment of eutrophication using ecological floating beds.

Effects of prey trophic mode on the gross-growth efficiency of marine copepods: the case of mixoplankton

Copepod reproductive success largely depends on food quality, which also reflects the prey trophic mode. As such, modelling simulations postulate a trophic enhancement to higher trophic levels when mixotrophy is accounted in planktonic trophodynamics. Here, we tested whether photo-phagotrophic protists (mixoplankton) could enhance copepod gross-growth efficiency by nutrient upgrading mechanisms compared to obligate autotrophs and heterotrophs. To validate the hypothesis, we compared physiological rates of the copepod Paracartia grani under the three functional nutrition types. Ingestion and egg production rates varied depending on prey size and species, regardless of the diet. The gross-growth efficiency was variable and not significantly different across nutritional treatments, ranging from 3 to 25% in the mixoplanktonic diet compared to autotrophic (11–36%) and heterotrophic (8–38%) nutrition. Egg hatching and egestion rates were generally unaffected by diet. Overall, P. grani physiological rates did not differ under the tested nutrition types due to the large species-specific variation within trophic mode. However, when we focused on a single species, Karlodinium veneficum, tested as prey under contrasting trophic modes, the actively feeding dinoflagellate boosted the egestion rate and decreased the copepod gross-growth efficiency compared to the autotrophic ones, suggesting possible involvement of toxins in modulating trophodynamics other than stoichiometric constraints.

Urban groundwater dissolved silica concentrations are elevated due to vertical composition of historic land-filling

Human influences on global silicon (Si) cycling include land-use change, deforestation, and wastewater discharge. Here we quantified the effect of urban expansion and historic land fill on dissolved silica (DSi) concentrations in urban groundwater in a northern temperate city. We hypothesized that historical land use, fill material, and urban infrastructure buried below cities create a unique anthropogenic geology which acts as a DSi source. We found that concentrations of DSi in urban groundwater are significantly higher than those from non-urban environments. We also found that historic land-use variables out-perform traditional topographic variables predicting urban DSi concentrations. We show that higher groundwater DSi concentrations result in increased subterranean groundwater discharge (SGD) fluxes, thereby altering coastal receiving water DSi availability. Further, we demonstrate that accounting for urban SGD DSi fluxes globally, could increase DSi SGD export by 20%. Together these results call for a re-evaluation of anthropogenic impacts on the global Si cycle.

Effects of Nylon Microplastic on Feeding, Lipid Accumulation, and Moulting in a Coldwater Copepod

Microplastic debris is a pervasive environmental contaminant that has the potential to impact the health of biota, although its modes of action remain somewhat unclear. The current study tested the hypothesis that exposure to fibrous and particulate microplastics would alter feeding, impacting on lipid accumulation, and normal development (e.g., growth, moulting) in an ecologically important coldwater copepod Calanus finmarchicus. Preadult copepods were incubated in seawater containing a mixed assemblage of cultured microalgae (control), with the addition of ∼50 microplastics mL^-1 of nylon microplastic granules (10-30 μm) or fibers (10 × 30 μm), which are similar in shape and size to the microalgal prey. The additive chemical profiles showed the presence of stabilizers, lubricants, monomer residues, and byproducts. Prey selectivity was significantly altered in copepods exposed to nylon fibers (ANOVA, P < 0.01) resulting in a nonsignificant 40% decrease in algal ingestion rates (ANOVA, P = 0.07), and copepods exposed to nylon granules showed nonsignificant lipid accumulation (ANOVA, P = 0.62). Both microplastics triggered premature moulting in juvenile copepods (Bernoulli GLM, P < 0.01). Our results emphasize that the shape and chemical profile of a microplastic can influence its bioavailability and toxicity, drawing attention to the importance of using environmentally relevant microplastics and chemically profiling plastics used in toxicity testing.

Water temperature drives phytoplankton blooms in coastal waters

Phytoplankton blooms are an important, widespread phenomenon in open oceans, coastal waters and freshwaters, supporting food webs and essential ecosystem services. Blooms are even more important in exploited coastal waters for maintaining high resource production. However, the environmental factors driving blooms in shallow productive coastal waters are still unclear, making it difficult to assess how environmental fluctuations influence bloom phenology and productivity. To gain insights into bloom phenology, Chl a fluorescence and meteorological and hydrological parameters were monitored at high-frequency (15 min) and nutrient concentrations and phytoplankton abundance and diversity, were monitored weekly in a typical Mediterranean shallow coastal system (Thau Lagoon). This study was carried out from winter to late spring in two successive years with different climatic conditions: 2014/2015 was typical, but the winter of 2015/2016 was the warmest on record. Rising water temperature was the main driver of phytoplankton blooms. However, blooms were sometimes correlated with winds and sometimes correlated with salinity, suggesting nutrients were supplied by water transport via winds, saltier seawater intake, rain and water flow events. This finding indicates the joint role of these factors in determining the success of phytoplankton blooms. Furthermore, interannual variability showed that winter water temperature was higher in 2016 than in 2015, resulting in lower phytoplankton biomass accumulation in the following spring. Moreover, the phytoplankton abundances and diversity also changed: cyanobacteria (< 1 μm), picoeukaryotes (< 1 μm) and nanoeukaryotes (3–6 μm) increased to the detriment of larger phytoplankton such as diatoms. Water temperature is a key factor affecting phytoplankton bloom dynamics in shallow productive coastal waters and could become crucial with future global warming by modifying bloom phenology and changing phytoplankton community structure, in turn affecting the entire food web and ecosystem services.

Physiological response of 10 phytoplankton species exposed to macondo oil and the dispersant, Corexit

Culture experiments were conducted on ten phytoplankton species to examine their biological and physiological responses during exposure to oil and a combination of oil and dispersant. The species tested included a range of taxa typically found in the Gulf of Mexico such as cyanobacteria, chlorophytes, and diatoms. Cultures were exposed to Macondo surrogate oil using the water accommodated fraction (WAF), and dispersed oil using a chemically enhanced WAF (CEWAF) and diluted CEWAF, to replicate conditions following the Deepwater Horizon spill in the Gulf of Mexico. A range of responses were observed, that could broadly class the algae as either "robust" or "sensitive" to oil and/or dispersant exposure. Robust algae were identified as Synechococcus elongatus, Dunaliella tertiolecta, two pennate diatoms Phaeodactylum tricornutum and Navicula sp., and Skeletonema grethae CCMP775, and were largely unaffected by any of the treatments (no changes to growth rate or time spent in lag phase relative to controls). The rest of the phytoplankton, all centric diatoms, exhibited at least some combination of reduced growth rates or increased lag time in response to oil and/or dispersant exposure. Photophysiology did not have a strong treatment effect, with significant inhibition of photosynthetic efficiency (F_v /F_m ) only observed in the CEWAF, if at all. We found that the effects of oil and dispersants on phytoplankton physiology were species-dependent, and not always detrimental. This has significant implications on how oil spills might impact phytoplankton community structure and bloom dynamics in the Gulf of Mexico, which in turn impacts higher trophic levels.

Investigating the impacts of treated effluent discharge on coastal water health (Visakhapatnam, SW coast of Bay of Bengal, India)

The present study investigated the impacts of treated effluent discharge on physicochemical and biological properties of coastal waters from three pharmaceuticals situated along the coast of Visakhapatnam (SW Bay of Bengal). Seawater samples were collected (during the months of December 2013, March 2014 and April 2014) from different sampling locations (Chippada (CHP), Tikkavanipalem (TKP) and Nakkapalli (NKP)) at 0- and 30-m depths within 2-km radius (0.5 km = inner, 1 km = middle and 2 km = outer sampling circles) from the marine outfall points. Physicochemical and biological parameters, which differed significantly within the stations, were likely to be influenced by strong seasonality rather than local discharge. Dissolved oxygen variability was tightly coupled with both physical and biological processes. Phytoplankton cell density and total chlorophyll (TChla) concentrations were significantly correlated with dissolved inorganic nutrient concentrations. CHP (December) represented a diatom bloom condition where the highest concentrations of diatom cells, total chlorophyll (TChla), dissolved oxygen coupled with lower zooplankton abundance and low nutrient levels were noticed. The centric diatom, Chaetoceros sp. (> 50%) dominated the phytoplankton community. TKP (March) represented a post-diatom bloom phase with the dominance of Pseudo-nitzschia seriata; zooplankton abundance and nutrient concentrations were minimum. Conversely, NKP (April) represented a warm well-stratified heterotrophic period with maximum zooplankton and minimum phytoplankton density. Dinoflagellate abundance increased at this station. Relatively higher water temperature, salinity, inorganic nutrients coupled with very low concentrations of dissolved oxygen, TChla and pH were observed at this station. Copepods dominated the zooplankton communities in all stations and showed their highest abundance in the innermost sampling circles. Treated effluent discharge did not seem to have any significant impact at these discharge points.

Fate and Effect of Dissolved Silicon within Wastewater Treatment Effluent

In large rivers, the ratios of silicon (Si)/nitrogen (N)/phosphorus (P) have changed dramatically as anthropogenic additions of N or P are not matched by Si. Wastewater effluent is a recognized source of N and P to coastal environments. Few previous studies, however, have examined the Si load of a large wastewater plant's effluent or the molar ratios of Si/N and Si/P in effluent. We examine the annual flux of dissolved silicon (DSi) carried by effluent from the second largest treatment plant by flow in the United States (Deer Island Treatment Plant, DITP, Boston, MA). We compare treatment plant nutrient fluxes to local urban river nutrient fluxes and trace the impact of the DITP DSi loading on receiving waters. Estimates (±95% confidence interval) of treated effluent (67 800 ± 1500 kmol DSi year^-1) compared to untreated (69 500 kmol DSi year^-1) indicate that the process of sewage treatment at DITP likely does not remove DSi. DITP effluent was Si-limited and this Si-limitation is reflected in the receiving waters (Massachusetts Bay). However, Si-limitation appears only in the area immediately surrounding the effluent discharge. We use these results to explain phytoplankton patterns in Massachusetts Bay and to provide the first estimate of DSi loading (3.6 Gmol SiO₂ year^-1) from wastewater effluent across the US.

Elemental composition, distribution and control of biogenic silica in the anthropogenically disturbed and pristine zone inter-tidal sediments of Indian Sundarbans mangrove-estuarine complex

Spatial distribution and interrelationship among organic nutrients - silica and carbon - and various lithogenic elements were investigated in the surficial sediments of Matla estuary and Core Zone of Indian Sundarbans Reserve Forest using spatial analysis and multivariate statistics. Biogenic silica (BSi), an important parameter for coastal biogeochemisry, was measured using Si-time alkaline leaching method. BSi concentration ranged from 0.01% to 0.85% with higher concentrations in upstream region of Matla estuary and attenuated values towards the bay, seemingly due to changes in hydrodynamics and land use conditions. Spatial distribution of BSi did not exhibit significant correlation with sediment parameters of organic carbon (OC), elemental composition and clay content. However, it showed significant contrasting trends with total phosphorus (TP) and total silica of human influenced Matla estuary sediments as well as the dissolved silica (DSi) of its surface waters. Anthropogenic influence on sediment geochemistry is discernable with the presence of higher concentrations of organic and inorganic elements in Matla estuary than in Core Zone sediments. Spatial variation trends are often challenging to interpret due to multiple sources of input, varying energy and salinity conditions and constant physical, chemical and biological alterations occurring in the environment. Nonetheless, it is certain that anthropogenic activities have a substantial influence on biogeochemical processes of Sundarbans mangrove-estuarine complex and potentially the coastal ocean.

Simulated terrestrial runoff triggered a phytoplankton succession and changed seston stoichiometry in coastal lagoon mesocosms

Climate change scenarios predict intensified terrestrial storm runoff, providing coastal ecosystems with large nutrient pulses and increased turbidity, with unknown consequences for the phytoplankton community. We conducted a 12-day mesocosm experiment in the Mediterranean Thau Lagoon (France), adding soil (simulated runoff) and fish (different food webs) in a 2 × 2 full factorial design and monitored phytoplankton composition, shade adaptation and stoichiometry. Diatoms (Chaetoceros) increased four-fold immediately after soil addition, prymnesiophytes and dinoflagellates peaked after six- and 12 days, respectively. Soil induced no phytoplankton shade adaptation. Fish reduced the positive soil effect on dinoflagellates (Scripsiella, Glenodinium), and diatom abundance in general. Phytoplankton community composition drove seston stoichiometry. In conclusion, pulsed terrestrial runoff can cause rapid, low quality (high carbon: nutrient) diatom blooms. However, bloom duration may be short and reduced in magnitude by fish. Thus, climate change may shift shallow coastal ecosystems towards famine or feast dynamics.

New oxylipins produced at the end of a diatom bloom and their effects on copepod reproductive success and gene expression levels

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy to higher trophic levels. However, these unicellular organisms produce secondary metabolites deriving from the oxidation of fatty acids, collectively termed oxylipins, with negative effects on predators, such as copepods, that feed on them (e.g. reduction in survival, egg production and hatching success) and, indirectly, on higher trophic levels. Here, a multidisciplinary study (oxylipin measurements, copepod fitness, gene expression analyses, chlorophyll distribution, phytoplankton composition, physico-chemical characteristics) was carried out at the end of the spring diatom bloom in April 2011 in the Northern Adriatic Sea (Mediterranean Sea) in order to deeply investigate copepod-diatom interactions, chemical communication and response pathways. The results show that the transect with the lowest phytoplankton abundance had the lowest copepod egg production and hatching success, but the highest oxylipin concentrations. In addition, copepods in both the analyzed transects showed increased expression levels of key stress-related genes (e.g. heat-shock proteins, catalase, glutathione S-transferase, aldehyde dehydrogenase) compared to control laboratory conditions where copepods were fed with the dinoflagellate Prorocentrum minimum which does not produce any oxylipins. New oxylipins that have never been reported before for microalgae are described for the first time, giving new insights into the complex nature of plant-animal signaling and communication pathways at sea. This is also the first study providing insights on the copepod response during a diatom bloom at the molecular level.

Urban Dissolved Silica: Quantifying the Role of Groundwater and Runoff in Wastewater Influent

Human impacts on silicon (Si) cycling are just being explored. In particular, we know little about the role of urban environments in altering the flux of Si from land to sea. Here we describe the annual load of dissolved Si (DSi) in the influent of the second largest wastewater treatment plant (by volume) in the United States (Deer Island Wastewater Facility, Boston, MA). We partition the ∼69 500 kmol DSi year(-1) influent load between three sources: runoff (12%), groundwater infiltration (39%), and sewage (49%). Based on these results, we hypothesized that instead of being delivered to local rivers, DSi in groundwater and runoff is redirected to the combined stormwater-sewage overflow system. To test this hypothesis we compared long-term (2007-2012) observations of DSi flux from the three urban rivers surrounding Boston to modeled DSi fluxes based on land use and land cover. As predicted, the modeled fluxes were higher than the measured fluxes indicating that the sewage infrastructure of Boston diverts watershed DSi to the treatment plant. This research increases our understanding of human changes to the Si cycle, demonstrates the potential usefulness of DSi as a groundwater infiltration tracer within sewage treatment systems, and highlights the underappreciated interannual variability of riverine DSi fluxes.

In vivo exposure to northern diatoms arrests sea urchin embryonic development

There are numerous reports indicating that marine diatoms may act harmful to early developmental stages of invertebrates. It is believed that the compounds responsible for these detrimental effects are oxylipins resulting from oxidized polyunsaturated fatty acids, and that they may function as grazing deterrents. Most studies reporting these effects have exposed test organisms to diatom extracts or purified toxins, but data from in vivo exposure to intact diatoms are scarce. We have conducted sea urchin egg incubation and plutei feeding experiments to test if intact diatom cells affected sea urchin embryo development and survival. This was done by exposing the common northern sea urchins Strongylocentrotus droebachiensis and Echinus acutus to northern strains of the diatoms Chaetoceros socialis, Skeletonema marinoi, Chaetoceros furcellatus, Attheya longicornis, Thalassiosira gravida and Porosira glacialis. The intact diatom cell suspensions were found to inhibit sea urchin egg hatching and embryogenesis. S. marinoi was the most potent one as it caused acute mortality in S. droebachiensis eggs after only four hours exposure to high (50 μg/L Chla) diatom concentrations, as well as 24 h exposure to normal (20 μg/L Chla) and high diatom concentrations. The second most potent species was T. gravida that caused acute mortality after 24 h exposure to both diatom concentrations. A. longicornis was the least harmful of the diatom species in terms of embryo development arrestment, and it was the species that was most actively ingested by S. droebachiensis plutei.

Low-Molecular-Weight Metabolites from Diatoms: Structures, Biological Roles and Biosynthesis

Diatoms are abundant and important biological components of the marine environment that biosynthesize diverse natural products. These microalgae are rich in various lipids, carotenoids, sterols and isoprenoids, some of them containing toxins and other metabolites. Several groups of diatom natural products have attracted great interest due to their potential practical application as energy sources (biofuel), valuable food constituents, and prospective materials for nanotechnology. In addition, hydrocarbons, which are used in climate reconstruction, polyamines which participate in biomineralization, new apoptotic agents against tumor cells, attractants and deterrents that regulate the biochemical communications between marine species in seawaters have also been isolated from diatoms. However, chemical studies on these microalgae are complicated by difficulties, connected with obtaining their biomass, and the influence of nutrients and contaminators in their environment as well as by seasonal and climatic factors on the biosynthesis of the corresponding natural products. Overall, the number of chemically studied diatoms is lower than that of other algae, but further studies, particularly those connected with improvements in the isolation and structure elucidation technique as well as the genomics of diatoms, promise both to increase the number of studied species with isolated biologically active natural products and to provide a clearer perception of their biosynthesis.

Assessing the in situ fertilization status of two marine copepod species, Temora longicornis and Eurytemora herdmani; how common are unfertilized eggs in nature?

We utilized an egg staining technique to measure the in situ fertilization success of two marine copepod species, Temora longicornis and Eurytemora herdmani from May to October 2008 in coastal Maine and correlated fertilization success with environmental conditions in their habitat. T. longicornis is a free spawning species that releases eggs into the ambient seawater after mating. In contrast, E. herdmani carries eggs in an egg sac until they hatch. The proportion of fertilized eggs within E. herdmani egg sacs was significantly higher than the freely spawned clutches of T. longicornis. This may be a result of the asymmetrical costs associated with carrying vs. spawning unfertilized eggs. T. longicornis frequently laid both fertilized and unfertilized eggs within their clutch. T. longicornis fertilization was negatively associated with chlorophyll concentration and positively associated with population density in their local habitat. The fertilization status of E. herdmani egg sacs was high throughout the season, but the proportion of ovigerous females was negatively associated with an interaction between predators and the proportion of females in the population. This study emphasizes that, in addition to population level processes, community and ecosystem level processes strongly influence the fertilization success and subsequent productivity of copepods.

Seasonal dynamics of Daphnia laevisBirge, 1878 ephippia in a tropical lake with a description of a new methodology for in situ evaluation

The effect of dormancy in zooplankton populations is still unknown, largely because of the lack of methods to estimate hatching and production of the dormant stages. This study aimed to compare the production and hatching rates of ephippia of Daphnia laevis between thermal stratification and mixing periods in Jacaré Lake (Middle Rio Doce, Minas Gerais, Brazil). For this, we collected ephippia on the sediment with core sampler and we created a device called the “Ephippial Collector”. There was a significant difference in ephippia hatching in situ between stratification and mixing periods (Pearson's Chi-squared test p <0.001), being higher in the second one. Significant differences in the hatching rates between periods was observed in the laboratory only for ephippia collected with Ephippial Collectors (Pearson's Chi-squared test p <0.001), being higher during the mixing period (∼8%). The core sample allows the collection of a certain fraction of the sediment that may contain a mixture of ephippia produced in different periods, i.e., may contain old and not viable ephippia, which masks the hatching rate. Thus, seasonality in hatching rates of ephippia was reported only by Ephippial Collectors. The higher hatching rate observed during the mixing period in the lake suggests that individuals hatched from ephippia may contribute to the increase in the population of D. laevis in the water column at this time.

Parasitic chytrids sustain zooplankton growth during inedible algal bloom

This study assesses the quantitative impact of parasitic chytrids on the planktonic food web of two contrasting freshwater lakes during different algal bloom situations. Carbon-based food web models were used to investigate the effects of chytrids during the spring diatom bloom in Lake Pavin (oligo-mesotrophic) and the autumn cyanobacteria bloom in Lake Aydat (eutrophic). Linear inverse modeling was employed to estimate undetermined flows in both lakes. The Monte Carlo Markov chain linear inverse modeling procedure provided estimates of the ranges of model-derived fluxes. Model results confirm recent theories on the impact of parasites on food web function through grazers and recyclers. During blooms of "inedible" algae (unexploited by planktonic herbivores), the epidemic growth of chytrids channeled 19-20% of the primary production in both lakes through the production of grazer exploitable zoospores. The parasitic throughput represented 50% and 57% of the zooplankton diet, respectively, in the oligo-mesotrophic and in the eutrophic lakes. Parasites also affected ecological network properties such as longer carbon path lengths and loop strength, and contributed to increase the stability of the aquatic food web, notably in the oligo-mesotrophic Lake Pavin.

Geospatial variability in the autumn community structure of epipelagic zooplankton in the upper layer of the northern South China Sea

Background

For the present study, we collected mesozooplankton in the upper layer (above 100 m in depth) of four stations in the northern South China Sea (SCS) to determine the influence of different water masses on their distribution and abundance from 27 September to 2 October 1999.

Results

In total, 18 major zooplankton taxa were recovered from the samples. Calanoid copepods, Noctilucales, and chaetognaths were dominant and together comprised 65.90% of the overall zooplankton counts. Zooplankton densities ranged from 102.19 to 1,285.24 individuals per cubic meters (ind./m3) (average, 306.38 ± 435.71). Noctilucales were abundant at stations located in the Kuroshio Current (KC) intrusion area. Integrating all samples, 32 copepod species were identified consisting of 23 genera belonging to 16 families. Total copepod abundances ranged from 30.24 to 311.17 ind./m3 (average, 99.14 ± 97.84). Numerically, Pleuromamma gracilis, Nannocalanus minor, and Lucicutia flavicornis were the most dominant species. The most frequently occurring species in all samples were Acartia (Acartia) negligens and Corycaeus (Farranula) gibbula. Results of a cluster analysis indicated that community structures of zooplankton and copepods of the northern SCS varied at geospatial scales during the sampling period.

Conclusions

Results of the present study suggest that the composition and community structure of zooplankton and copepods were influenced by intrusion of the KC in the shallow layer above 100 m in depth in the northern SCS. Some indicator species characteristic of the KC indicated that the study area received water masses from the northern SCS and the KC.

Remote sensing the phytoplankton seasonal succession of the Red Sea

The Red Sea holds one of the most diverse marine ecosystems, primarily due to coral reefs. However, knowledge on large-scale phytoplankton dynamics is limited. Analysis of a 10-year high resolution Chlorophyll-a (Chl-a) dataset, along with remotely-sensed sea surface temperature and wind, provided a detailed description of the spatiotemporal seasonal succession of phytoplankton biomass in the Red Sea. Based on MODIS (Moderate-resolution Imaging Spectroradiometer) data, four distinct Red Sea provinces and seasons are suggested, covering the major patterns of surface phytoplankton production. The Red Sea Chl-a depicts a distinct seasonality with maximum concentrations seen during the winter time (attributed to vertical mixing in the north and wind-induced horizontal intrusion of nutrient-rich water in the south), and minimum concentrations during the summer (associated with strong seasonal stratification). The initiation of the seasonal succession occurs in autumn and lasts until early spring. However, weekly Chl-a seasonal succession data revealed that during the month of June, consistent anti-cyclonic eddies transfer nutrients and/or Chl-a to the open waters of the central Red Sea. This phenomenon occurs during the stratified nutrient depleted season, and thus could provide an important source of nutrients to the open waters. Remotely-sensed synoptic observations highlight that Chl-a does not increase regularly from north to south as previously thought. The Northern part of the Central Red Sea province appears to be the most oligotrophic area (opposed to southern and northern domains). This is likely due to the absence of strong mixing, which is apparent at the northern end of the Red Sea, and low nutrient intrusion in comparison with the southern end. Although the Red Sea is considered an oligotrophic sea, sporadic blooms occur that reach mesotrophic levels. The water temperature and the prevailing winds control the nutrient concentrations within the euphotic zone and enable the horizontal transportation of nutrients.

Copepod population-specific response to a toxic diatom diet

Diatoms are key phytoplankton organisms and one of the main primary producers in aquatic ecosystems. However, many diatom species produce a series of secondary metabolites, collectively termed oxylipins, that disrupt development in the offspring of grazers, such as copepods, that feed on these unicellular algae. We hypothesized that different populations of copepods may deal differently with the same oxylipin-producing diatom diet. Here we provide comparative studies of expression level analyses of selected genes of interest for three Calanus helgolandicus populations (North Sea, Atlantic Ocean and Mediterranean Sea) exposed to the same strain of the oxylipin-producing diatom Skeletonema marinoi using as control algae the flagellate Rhodomonas baltica. Expression levels of detoxification enzymes and stress proteins (e.g. glutathione S-transferase, glutathione synthase, superoxide dismutase, catalase, aldehyde dehydrogenases and heat shock proteins) and proteins involved in apoptosis regulation and cell cycle progression were analyzed in copepods after both 24 and 48 hours of feeding on the diatom or on a control diet. Strong differences occurred among copepod populations, with the Mediterranean population of C. helgolandicus being more susceptible to the toxic diet compared to the others. This study opens new perspectives for understanding copepod population-specific responses to diatom toxins and may help in underpinning the cellular mechanisms underlying copepod toxicity during diatom blooms.

Molecular evidence of the toxic effects of diatom diets on gene expression patterns in copepods

BACKGROUND

Diatoms are dominant photosynthetic organisms in the world's oceans and are considered essential in the transfer of energy through marine food chains. However, these unicellular plants at times produce secondary metabolites such as polyunsaturated aldehydes and other products deriving from the oxidation of fatty acids that are collectively termed oxylipins. These cytotoxic compounds are responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment in marine organisms such as crustacean copepods.

PRINCIPAL FINDINGS

Here we show that two days of feeding on a strong oxylipin-producing diatom (Skeletonema marinoi) is sufficient to inhibit a series of genes involved in aldehyde detoxification, apoptosis, cytoskeleton structure and stress response in the copepod Calanus helgolandicus. Of the 18 transcripts analyzed by RT-qPCR at least 50% were strongly down-regulated (aldehyde dehydrogenase 9, 8 and 6, cellular apoptosis susceptibility and inhibitor of apoptosis IAP proteins, heat shock protein 40, alpha- and beta-tubulins) compared to animals fed on a weak oxylipin-producing diet (Chaetoceros socialis) which showed no changes in gene expression profiles.

CONCLUSIONS

Our results provide molecular evidence of the toxic effects of strong oxylipin-producing diatoms on grazers, showing that primary defense systems that should be activated to protect copepods against toxic algae can be inhibited. On the other hand other classical detoxification genes (glutathione S-transferase, superoxide dismutase, catalase, cytochrome P450) were not affected possibly due to short exposure times. Given the importance of diatom blooms in nutrient-rich aquatic environments these results offer a plausible explanation for the inefficient use of a potentially valuable food resource, the spring diatom bloom, by some copepod species.

PLASTICITY OF OXYLIPIN METABOLISM AMONG CLONES OF THE MARINE DIATOM SKELETONEMA MARINOI (BACILLARIOPHYCEAE)(1)

Diatom oxylipins have been observed to deleteriously impact copepod reproductive success. However, field studies have revealed very variable and case-dependent results. Therefore, the plasticity of diatom oxylipin metabolism was studied among four clones of the marine diatom Skeletonema marinoi Sarno et Zingone. Diatom oxylipin metabolism was studied by two lipoxygenase (LOX) activity assays carried out at different pH values and by oxylipin quantification. The four clones showed no major metabolic differences in terms of protein content or growth rate. However, two of the clones produced significantly higher levels of oxylipins than the other two. LOX activity measurements also indicated clonal variability in fatty acid oxidative metabolism. The presence of clone-specific differences in oxylipin metabolism may play a role in shaping diatom population dynamics by conferring selective advantages to certain clones.

Strain-related physiological and behavioral effects of Skeletonema marinoi on three common planktonic copepods

Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA) and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects. Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology, which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds and their potential implications on different copepod species.

LIPOXYGENASE PRODUCTS IN MARINE DIATOMS: A CONCISE ANALYTICAL METHOD TO EXPLORE THE FUNCTIONAL POTENTIAL OF OXYLIPINS(1)

Oxylipins are oxygenated derivatives of polyunsaturated fatty acids (PUFAs) that act as chemical mediators in many ecological and physiological processes in marine and freshwater diatoms. The occurrence and distribution of these molecules are relatively widespread within the lineage with considerable species-specific differences due to the variability of both the fatty acids recognized as substrates and the enzymatic transformations. The present review provides a general introduction to recent studies on diatom oxylipins and describes an analytical method for the detection and assessment of these elusive molecules in laboratory and field samples. This methodology is based on selective enrichment of the oxylipin fraction by solvent extraction, followed by parallel acquisition of full-scan UV and tandem mass spectra on reverse phase liquid chromatography (LC) peaks. The analytical procedure enables identification of potential genetic differences, enzymatic regulation, and ecophysiological conditions that result in different oxylipin signatures, thus providing an effective tool for probing the functional relevance of this class of lipids in plankton communities. Examples of oxylipin measurements in field samples are also provided as a demonstration of the analytical potential of the methodology.

Toxigenic effects of diatoms on grazers, phytoplankton and other microbes: a review

Traditionally, diatoms have been regarded as providing the bulk of the food that sustains the marine food chain and important fisheries. However, this view was challenged almost two decades ago on the basis of laboratory and field studies showing that when copepods, the principal predators of diatoms, feed on certain diatom diets, they produce abnormal eggs that either fail to develop to hatching or hatch into malformed (i.e. teratogenic) nauplii that die soon afterwards. Over the years, many explanations have been advanced to explain the causes for reproductive failure in copepods and other marine and freshwater invertebrates including diatom toxicity, or nutritional deficiency and poor assimilation of essential compounds in the animal gut. Here we review the literature concerning the first possibility, that diatoms produce cytotoxic compounds responsible for growth inhibition and teratogenic activity, potentially sabotaging future generations of grazers by inducing poor recruitment. The cytotoxic compounds responsible for these effects are short chain polyunsaturated aldehydes (PUAs) and other oxygenated fatty acid degradation products such as hydroxides, oxo-acids, and epoxyalcohols (collectively termed oxylipins) that are cleaved from fatty acid precursors by enzymes activated within seconds after crushing of cells. Such toxins are suggested to have multiple simultaneous functions in that they not only deter herbivore feeding but some also act as allelopathic agents against other phytoplankton cells, thereby affecting the growth of competitors, and also signalling population-level cell death and termination of blooms, with possible consequences for food web structure and community composition. Some oxylipins also play a role in driving marine bacterial community diversity, with neutral, positive or negative interactions depending on the species, thereby shaping the structure of bacterial communities during diatom blooms. Several reviews have already been published on diatom-grazer interactions so this paper does not attempt to provide a comprehensive overview, but rather to consider some of the more recent findings in this field. We also consider the role of diatom oxylipins in mediating physiological and ecological processes in the plankton and the multiple simultaneous functions of these secondary metabolites.

Genome-wide analysis of the diatom cell cycle unveils a novel type of cyclins involved in environmental signaling

BACKGROUND

Despite the enormous importance of diatoms in aquatic ecosystems and their broad industrial potential, little is known about their life cycle control. Diatoms typically inhabit rapidly changing and unstable environments, suggesting that cell cycle regulation in diatoms must have evolved to adequately integrate various environmental signals. The recent genome sequencing of Thalassiosira pseudonana and Phaeodactylum tricornutum allows us to explore the molecular conservation of cell cycle regulation in diatoms.

RESULTS

By profile-based annotation of cell cycle genes, counterparts of conserved as well as new regulators were identified in T. pseudonana and P. tricornutum. In particular, the cyclin gene family was found to be expanded extensively compared to that of other eukaryotes and a novel type of cyclins was discovered, the diatom-specific cyclins. We established a synchronization method for P. tricornutum that enabled assignment of the different annotated genes to specific cell cycle phase transitions. The diatom-specific cyclins are predominantly expressed at the G1-to-S transition and some respond to phosphate availability, hinting at a role in connecting cell division to environmental stimuli.

CONCLUSION

The discovery of highly conserved and new cell cycle regulators suggests the evolution of unique control mechanisms for diatom cell division, probably contributing to their ability to adapt and survive under highly fluctuating environmental conditions.

The influence of bioactive oxylipins from marine diatoms on invertebrate reproduction and development

Diatoms are one of the main primary producers in aquatic ecosystems and occupy a vital link in the transfer of photosynthetically-fixed carbon through aquatic food webs. Diatoms produce an array of biologically-active metabolites, many of which have been attributed as a form of chemical defence and may offer potential as candidate marine drugs. Of considerable interest are molecules belonging to the oxylipin family which are broadly disruptive to reproductive and developmental processes. The range of reproductive impacts includes; oocyte maturation; sperm motility; fertilization; embryogenesis and larval competence. Much of the observed bioactivity may be ascribed to disruption of intracellular calcium signalling, induction of cytoskeletal instability and promotion of apoptotic pathways. From an ecological perspective, the primary interest in diatom-oxylipins is in relation to the potential impact on energy flow in planktonic systems whereby the reproductive success of copepods (the main grazers of diatoms) is compromised. Much data exists providing evidence for and against diatom reproductive effects; however detailed knowledge of the physiological and molecular processes involved remains poor. This paper provides a review of the current state of knowledge of the mechanistic impacts of diatom-oxylipins on marine invertebrate reproduction and development.

Tetrahedral Zinc Complexes with Liquid Crystalline and Luminescent Properties: Interplay Between Nonconventional Molecular Shapes and Supramolecular Mesomorphic Order

Novel metallomesogens with luminescent properties and liquid crystalline behavior at room temperature have been achieved by the preparation of zinc complexes with polycatenar pyrazole and bis(pyrazolyl)methane ligands. Their molecular structures do not have a conventional shape in that they are far from the typical rod-like and flat disc-like geometries of common liquid crystals. They consist of a nonplanar nucleus due to the methylene spacer and/or the coordination to the tetrahedral center, as confirmed by single crystal analysis of the cores. The different numbers and positions of side chains in the pyrazole ligand enabled us to access lamellar and columnar mesophases and, of particular interest, to obtain columnar arrangements at room temperature. Supramolecular models for the organization of the molecules in the mesophases are proposed on the basis of the small-angle XRD diffractograms. The zinc complexes display luminescence in the near UV-blue region with large Stokes shifts. An interplay between non-conventional molecular shapes (due to the tetrahedral core) and the supramolecular mesomorphic order (due to the ligand design) led to materials that interestingly embody two rather opposite properties, a columnar self-organizational ability and luminescence with weak intermolecular interactions.

Lipid and Fatty Acid Composition of Diatoms Revisited: Rapid Wound-Activated Change of Food Quality Parameters Influences Herbivorous Copepod Reproductive Success

Lipid and fatty acid composition are considered to be key parameters that determine the nutritive quality of phytoplankton diets for zooplanktonic herbivores. The fitness, reproduction and physiology of the grazers are influenced by these factors. The trophic transfer of lipids and fatty acids from algal cells has been typically studied by using simple extraction and quantification approaches, which, as we argue here, do not reflect the actual situation in the plankton. We show that cell disruption, as it occurs during a predator's grazing on diatoms can drastically change the lipid and fatty acid content of the food. In some algae, a rapid depletion of polyunsaturated fatty acids (PUFAs) is observed within the first minutes after cell disruption. This fatty acid depletion is directly linked to the production of PUFA-derived polyunsaturated aldehydes (PUA); these are molecules that are thought to be involved in the chemical defence of the algae. PUA-releasing diatoms are even capable of transforming lipids from other sources if these are available in the vicinity of the wounded cells. Fluorescent staining reveals that the enzymes involved in lipid transformation are active in the foregut of copepods, and therefore link the depletion processes directly to food uptake. Incubation experiments with the calanoid copepod Temora longicornis showed that PUFA depletion in PUA-producing diatoms is correlated to reduced hatching success, and can be compensated for by externally added single fatty acids.

Multicompartment micelles from hyperbranched star-block copolymers containing polycations and fluoropolymer segment

In this Article, we have investigated the self-assembly of a series of amphiphilic hyperbranched star-block copolymers to form multicompartment micelles in acidic aqueous solution (pH 3.0) or in a dimethylformamide/water (pH 3.0) mixture. These hyperbranched star-block copolymers were prepared via oxyanion-initiated polymerization process, using hydroxyl-terminated hyperbranched poly[3-ethyl-3-(hydroxymethyl)oxetane] (HP) as a macroinitiator precursor with multi-reactive sites. It was turned into oxyanion end-capped macroinitiator through the reaction with potassium hydride, and followed by a sequential addition of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) and 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (OFPMA). The resultant HP-star-PDMAEMA-b-POFPMA copolymers were characterized via 1H NMR, 19F NMR, and gel permeation chromatography (GPC). The analyses of transmission electron microscopy (TEM), dynamic light scattering (DLS), and microelectrophoresis confirmed that these copolymers could directly self-organize into supramolecular multicompartment micelles with different diameters, depending on the length of the PDMAEMA segment, which can be protonated in acidic aqueous medium. The measurement of the zeta potential gave further evidence of the aggregating structures for the multicompartment micelles.

Helical Pores Self-Assembled from Homochiral Dendritic Dipeptides Based on l-Tyr and Nonpolar α-Amino Acids

The synthesis of dendritic dipeptides (4-3,4-3,5)12G2-CH2-Boc-L-Tyr-X-OMe where X = Gly, L-Val, L-Leu, L-Ile, L-Phe, and L-Pro is reported. Their self-assembly in bulk and in solution and the structural and retrostructural analysis of their periodic assemblies were compared to those of the previously reported and currently reinvestigated dendritic dipeptides with X = L-Ala. All dendritic dipeptides containing as X nonpolar alpha-amino acids self-assemble into helical porous columns. The substituent of X programs the structure of the helical pore and the resulting periodic array, in spite of the fact that its molar mass represents only between 0.05 and 4.77% from the molar mass of the dendritic dipeptide. In addition to the various 2-D columnar lattices, the dendritic dipeptides based on L-Ala, L-Leu, and L-Phe self-organize into 3-D hexagonal columnar crystals while those based on L-Val and L-Ile into an unknown columnar crystal. The principles via which the aliphatic and aromatic substituents of X program the structure of the helical pores indicate synthetic pathways to helical pores with bioinspired functions based on artificial nonpolar alpha-amino acids.

Rings of single-walled carbon nanotubes: molecular-template directed assembly and Monte Carlo modeling

Rings of single-walled carbon nanotubes (SWNTs) were assembled by dip-pen nanolithography (DPN) generated molecular templates consisting of COOH-terminated monolayers in circular patterns surrounded by passivating CH3-terminated SAMs. Experimental data and atomic-level Monte Carlo simulations show that SWNTs assemble into rings with radii as small as 100 nm at the edge of the COOH templates. This directed assembly is strongly length-dependent; only when the length of a SWNT is longer than half of the circumference of the circle does the SWNT bend to precisely follow the interface of the COOH-terminated monolayer. The theoretical modeling shows that the strain energy of each SWNT is balanced by the energy difference between the van der Waals interactions of the tube with COOH and CH3 templates to produce the resulting ring structure.

Chemistry of oxylipin pathways in marine diatoms

Oxylipins are important signal transduction molecules widely distributed in animals and plants where they regulate a variety of events associated with physiological and pathological processes. The family embraces several different metabolites that share a common origin from the oxygenase-catalyzed oxidation of polyunsaturated fatty acids. The biological role of these compounds has been especially studied in mammalians and higher plants, although a varied and very high concentration of these products has also been reported from marine macroalgae. This article gives a summary of our results concerning the oxylipin chemistry of marine diatoms, a major class of planktonic microalgae that discourage predation from their natural grazers, zooplanktonic copepods, using chemical warfare. These apparently harmless microscopic cells produce a plethora of oxylipins, including short-chain unsaturated aldehydes, hydroxyl-, keto-, and epoxyhydroxy fatty acid derivatives, that induce reproductive failure in copepods through abortions, congenital malformations, and reduced larval growth. The biochemical process involved in the production of these compounds shows a simple regulation based on decompartmentation and mixing of preexisting enzymes and requires hydrolysis of chloroplast-derived glycolipids to feed the downstream activities of C16 and C20 lipoxygenases.

From plankton to top predators: bottom-up control of a marine food web across four trophic levels

1. Abundant mid-trophic pelagic fish often play a central role in marine ecosystems, both as links between zooplankton and top predators and as important fishery targets. In the North Sea, the lesser sandeel occupies this position, being the main prey of many bird, mammal and fish predators and the target of a major industrial fishery. However, since 2003, sandeel landings have decreased by > 50%, and many sandeel-dependent seabirds experienced breeding failures in 2004. 2. Despite the major economic implications, current understanding of the regulation of key constituents of this ecosystem is poor. Sandeel abundance may be regulated 'bottom-up' by food abundance, often thought to be under climatic control, or 'top-down' by natural or fishery predation. We tested predictions from these two hypotheses by combining unique long-term data sets (1973-2003) on seabird breeding productivity from the Isle of May, SE Scotland, and plankton and fish larvae from the Continuous Plankton Recorder survey. We also tested whether seabird breeding productivity was more tightly linked to sandeel biomass or quality (size) of individual fish. 3. The biomass of larval sandeels increased two- to threefold over the study period and was positively associated with proxies of the abundance of their plankton prey. Breeding productivity of four seabirds bringing multiple prey items to their offspring was positively related to sandeel larval biomass with a 1-year lag, indicating dependence on 1-year-old fish, but in one species bringing individual fish it was strongly associated with the size of adult sandeels. 4. These links are consistent with bottom-up ecosystem regulation and, with evidence from previous studies, indicate how climate-driven changes in plankton communities can affect top predators and potentially human fisheries through the dynamics of key mid-trophic fish. However, the failing recruitment to adult sandeel stocks and the exceptionally low seabird breeding productivity in 2004 were not associated with low sandeel larval biomass in 2003, so other mechanisms (e.g. predation, lack of suitable food after metamorphosis) must have been important in this case. Understanding ecosystem regulation is extremely important for predicting the fate of keystone species, such as sandeels, and their predators.

Copepods induce paralytic shellfish toxin production in marine dinoflagellates

Among the thousands of unicellular phytoplankton species described in the sea, some frequently occurring and bloom-forming marine dinoflagellates are known to produce the potent neurotoxins causing paralytic shellfish poisoning. The natural function of these toxins is not clear, although they have been hypothesized to act as a chemical defence towards grazers. Here, we show that waterborne cues from the copepod Acartia tonsa induce paralytic shellfish toxin (PST) production in the harmful algal bloom-forming dinoflagellate Alexandrium minutum. Induced A. minutum contained up to 2.5 times more toxins than controls and was more resistant to further copepod grazing. Ingestion of non-toxic alternative prey was not affected by the presence of induced A. minutum. The ability of A. minutum to sense and respond to the presence of grazers by increased PST production and increased resistance to grazing may facilitate the formation of harmful algal blooms in the sea.

Selective Oxidative Cyclization by FeCl3 in the Construction of 10H-Indeno[1,2-b]triphenylene Skeletons in Polycyclic Aromatic Hydrocarbons

A novel family of polycyclic aromatic hydrocarbons of various shapes based on the 10H-indeno[1,2-b]triphenylene skeleton has been synthesized via a reaction sequence of Diels-Alder reaction, decarbonylation, followed by an oxidative cyclization. In particular, the reaction conditions for regioselective oxidative cyclization promoted by FeCl3 are investigated, and this reaction is employed as an effective method to afford the above molecules under mild conditions. Their photophysical properties in dilute solution are also reported.

Supramolecular Self-Assembly of Dendronized Polymers: Reversible Control of the Polymer Architectures through Acid−Base Reactions

Acid-base switchable supramolecular dendronized polyacetylenes (DPAs) with increasing steric bulk on going from generation one [G1] to three [G3], were constructed using multiple self-assembly processes between Fréchet-type [G1]-[G3]-dendritic dialkylammonium salts and a dibenzo[24]crown-8-containing polymer. The formation of the supramolecular systems is acid-base switchable to either an ON (rodlike dendronized polymers) or an OFF (flexible polymers) state. Thus, by controlling the superstructures of the supramolecular polymers with the [G1]-[G3] dendrons, it is possible to induce conformational changes within the polymer backbones. The supramolecular dendronized polymers, as well as their threading-dethreading properties, were characterized by (1)H NMR and UV absorption spectroscopies, gel permeation chromatography (GPC) and light scattering (LS). Independent measures of molecular weight (GPC, LS) indicate that DPAs behave as increasingly rigid macromolecules with each generation in solution. Molecular dynamics simulations of each DPA suggest that the lengths of the polymer backbones increase accordingly. Atomic force microscopy of the [G3]-dendronized polystyrene (DPS), as well as the DPAs, reveal surface morphologies indicative of aggregated superstructures.

Rapid Self-Assembly of Core−Shell Organosilicon Microcapsules within a Microfluidic Device

The preparation of hierarchically structured organosilicon microcapsules from commercially available starting materials is described. Using a microfluidic device, an emulsion of dichlorodiphenylsilane is formed in a continuous phase of aqueous glycerol. The silane droplets undergo hydrolysis, condensation, and crystallization within minutes to form self-assembled, core-shell microcapsules. The microparticles have been characterized with light and electron microscopy, nuclear magnetic resonance spectroscopy (NMR), diffusion-ordered NMR spectroscopy (DOSY), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). The characterization data show that the microcapsule walls consist of amorphous, oligomeric poly(diphenylsiloxane) surrounded by a spiny layer of crystalline diphenylsilanediol. Glycerol is occluded within the wall material but is not covalently bound to the silicon components. Glycerol is a crucial element for producing low-dispersity microcapsules with well-ordered surface spines, as the use of methyl cellulose as viscomodifier yields amorphous surfaces.